BACKGROUND
Inverters are widely used in every
aspect of life to provide electrical power for our daily activities.
Inverters are used in situation
where low voltage DC sources such as batteries and solar panels must be
converted to AC in other to power electrical appliances. One example of such situation
would be converting a DC Voltage from a car battery to power a laptop,
television, cell phones etc.
The method in which the low voltage DC power is converted to
AC is known as inversion. In this circuit a 12volts dc battery is being used
with some electronic components to convert the dc to ac, and a transformer is
used to step up the voltage to 220volts ac.
I know some people have been surfing the net in other to get
functional circuit diagrams but to no avail cause majority of the circuits on
the net are half way worked, some do not even work. Not to worry you’re at the
right place. At Eng Updates we avail to you functional circuits you could work
on for personal studies, research, DIY projects, degree projects etc. Just try
them and thank us latter.
CONSTRUCTION
Components needed
1. Resistors
2. Capacitors
3. Diodes
4. Inductor
5. Transistors
6. MOSFET
7. SG3525IC
8. NE555
timer
9. Relays
Circuit Diagram
Note:
the value of all the components is on the diagram
VR1 is used to set the output
frequency of the inverter
VR2 is used to set the output
voltage
VR3 is used to set the battery
low voltage shutdown
The tools and instruments used include:
1. Lead and Soldering Iron
2. Lead sucker
3. Cutter
4. Razor blade
5. Plier
6. Digital Multimeter
7. Vero and bread board
DETERMINATION OF THE OSCILLATING FREQUENCY
By supplying a 12Volt DC to
the IC SG 3525 PWM, the frequency of the oscillating signal was determined
using a 10KΩ variable resistor connected in series with another 56KΩ
resistor and both connected in parallel
with 0.22µF to form the RC time constant network.
Frequency,
F = 1/1.1*Ct*Rf where
Time Capacitor (CT) =
0.22µF
Fixed Resistor (RF) = 56KΩ
Variable Resistor (VR) =
10KΩ
Time Resistor (RT)
=56KΩ+10KΩ = 66KΩ
Therefore,
F=
1/1.1*0.22¯6*66k
F=
62.6Hz
It should be noted that the
potentiometer was varied till the frequency of the signal was 50Hz.
CALCULATION OF TRANSFORMER PARAMETERS
The power Rating for the Inverter transformer (KVA) =1.0KA , E2=12V
Assuming the efficiency of transformer =85%
Then Input rating =output /Efficiency=1000VA/0.85=1176VA
Ip = PI / VP VP = 260V
Ip = 1176 / 260 = 4.5A
Ip = Po / Vs Vs = 12V
Ip = 1000 / 12 = 83.3A
For practical design of inverter transformer
Number of turns per volt for both primary and secondary winding is given by;
NT per V= 7/A
Where A is the area of transformer former in sq. inch
Former area A is 2.3inch by 1.5inch = 3.45sq.inch
NT per V= 7/3.45=2.03
The power Rating for the Inverter transformer (KVA) =1.0KA , E2=12V
Assuming the efficiency of transformer =85%
Then Input rating =output /Efficiency=1000VA/0.85=1176VA
Ip = PI / VP VP = 260V
Ip = 1176 / 260 = 4.5A
Ip = Po / Vs Vs = 12V
Ip = 1000 / 12 = 83.3A
For practical design of inverter transformer
Number of turns per volt for both primary and secondary winding is given by;
NT per V= 7/A
Where A is the area of transformer former in sq. inch
Former area A is 2.3inch by 1.5inch = 3.45sq.inch
NT per V= 7/3.45=2.03
NT per V= 2 (approximate value).
Primary Winding
Charger tapping winding turns
Np1= NT per V * E1=220V
Np1 = 2 * 220 = 440turns
Inverter (out) tapping winding turns
NS2= NT per V * E3=260V
NS2 = 2 * 260= 520turns
Difference of Inverting and Charging turns = 520 – 440 = 80turns.
For the primary windings, charging tapping is brought out after 440 turns and an addition 80 turns is
made for the inverter output tapping.
Secondary Winding
Secondary turns Ns= NT per V * E2 = 12V
Ns= 2 *12= 24turns. (Bifilar winding)
Primary Winding
Charger tapping winding turns
Np1= NT per V * E1=220V
Np1 = 2 * 220 = 440turns
Inverter (out) tapping winding turns
NS2= NT per V * E3=260V
NS2 = 2 * 260= 520turns
Difference of Inverting and Charging turns = 520 – 440 = 80turns.
For the primary windings, charging tapping is brought out after 440 turns and an addition 80 turns is
made for the inverter output tapping.
Secondary Winding
Secondary turns Ns= NT per V * E2 = 12V
Ns= 2 *12= 24turns. (Bifilar winding)
SWG Estimation
Standard Gauge Weight, SGW, can be estimated as follow;
Considering conduction current density J (with fixed value of 2.5A/mm2) and windings coil current.
For Ip = 4.5A, the corresponding gauge from tables is 24SWG and
For Is = 83.3A, the corresponding gauge from tables is 13SWG
 |
| complete 3.5kva inverter with the same diagram but little modification on the power mosfet and transformer |
NOTE
The following maintenance
practices and safety precautions are suggested to improve the life span of the
system and prevent hazards to the users.
1. Dead batteries should
not be used with the inverter
2. The battery terminals
should not be removed too often. When it is removed, placement of correct
polarity must be ensured.
3. The inverter must be
kept in a moderate temperature environment.
4. The inverter should be
shut down when not in use.
5. The inverter should
always be partially loaded (not more than 75% of its maximum capacity).
6. The use of inductive
loads like refrigerator, induction machines etc. on this inverter (1KVA) should
be avoided, however inverters with much higher ratings can be used to power
appliances with much power usage.
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